Operating gas heater for thermal power plants



Jam. 24, 1950 R. RUEGG 2,495,550

OPERATING GAS HEATER FOR THERMAL POWER PLANTS Filed April 13, 1945 q nuankw 33 RwideM Rwagg Patented Jan. 24, 1950 OPERATING GAS HEATER FOR THERMAL POWER PLANTS Rudolf Ruegg, Zurich, Switzerland, assignor to Aktiengesellschaft Fuer Technische Studien, Zurich, Switzerland, a corporation of Switzerland Application April 13, 1945, Serial No. 588,186 In Switzerland May 26, 1944 7 Claims. 1

This invention relates to a gas heater primarily intended for use in a thermal power plant in which at least the greater part of a gaseous working medium, preferably air, describes a closed circuit, being raised to a higher pressure in at least one compressor, then brought to a higher temperature in a heater by an indirect supply of heat from an external source and thereafter expanded in at least one turbine. In power plants of this type it is known to arrange the heating surfaces of the heater in a num-, ber of passes and to supply part of the fuel to a combustion chamber situated in front of all heating surfaces and the remaining fuel to at least one further combustion chamber arranged between two of the heating surfaces, and further to return to the heater flue gases which have been branched off at any point beyond the heater.

In such plants the tendency is to obtain a given thermal output with a heating surface which is as small as possible, so that the manufacturing cost of the heater can be reduced to the utmost. This can be realized in the simplest manner by adopting the largest possible difference in temperature between the combustion gases and the working medium to be heated. To realize this it has already been proposed to introduce the fue1 into the heater not only at one point but at several points, the latter being effected partly between adjacent heating surfaces. In this case approximately the same temperature can be reached at all points of the heater where fuel is burnt and thus, as desired, a greater averagedifierence in temperature between the combustion gases and the working medium to be heated over a considerable range of the heater.

However, the adoption of a high temperature for the combustion gases is often limited by other requirements. For example in the case of fuels containing ash it is generally required that the temperature of the combustion gases at the inlet to the first heater tube nest be so low that a deposit of liquid ash on the heating surfaces is prevented with certainty. To bring about a reduction in the temperature of the combustion gases in front of the inlet to the heater tube nest it has further been proposed to mix these gases with returned flue gases. But the greater the quantity of flue gas that has to be returned, the greater also is the power consumed by the fan for circulating said portion of flu gas, which has a detrimental effect on the overall efliclency of the plant. To overcome this 2 drawback in a thermal power plant of the kind herein referred to, according to the present invention fiue gases are only returned to the combustion chambers arranged in front of all the heating surfaces, this possibility depending upon the fact that in the remaining combustion chambers the gases coming from the preceding heating surfaces are already capable of lowering the temperature of the combustion gases sufliciently to ensure that flue gases need not also be returned to these chambers.

In the accompanying drawing a preferred embodiment of a thermal power plant for carrying out the process according to the present invention is shown by Way of example and in a simplified mode of representation, those parts of the plant which constitute essential features of the invention being illustrated on an enlarged scale.

In the heater A illustrated in the figure heat from an external source is supplied to the air, since in conjunction with the illustrated embodiment it is assumed that air is used as working medium. This heater A comprises three combus tion chambers I, 2, 3 and three heating surfaces designed as tube nests 4, 5, 6. The tube nests 4, 5 and 6 are disposed in combustion-gas passes l, 8 and 9 respectively. The combustion chamber l is arranged in front of all tube nests 4, 5 and 6, whilst the combustion chamber 2 is situated between the two nests 4 and 5, which as regards the direction of flow of the flue gases are connected in series, and the combustion chamber 3 is situated between the two nests 5 and 6, which as regards the direction of flow of the flue gases are also connected in series. The com bustion chamber l arranged in front of all heating surfaces 5, 6, is situated before the lower part 'of the first tube nest 4, whilst the combustion chamber 2 is disposed between the upper parts of the two tube nests l, 5 and the combustion chamber 3 between the lower parts of the tube nests 5 and 6.

The air to be heated in heat'er'A enters through a pipe ID into tube nest 6 and flows from the latter through a pipe H into tube nest 5 and from this through a pipe 12 into tube nest 4, where it is heated to the required final temperature. The air heated in this manner passes through a pipe is into a turbine M, in which it expands, this turbine delivering power to a compressor l5 and a generator IS. The air issuing from turbine l4 passes through a pipe I! into a heat exchanger [8 where it gives up heat to that part of the air which flows from the compressor l5 through a pipe l9 and. this heat exchanger I8 into the pipe l connected to the tube nest 6. The expanded air cooled in the heat exchanger I8 passes through a pipe and cooler 33 into the compressor l5 wherein it is re-compressed to a higher pressure and then forced into said pipe l9.

A portion'of the flue gases is branched off behind the heater A at point 2| and returned by a fan 22, which is driven by a motor 23, into the combustion chamber I. A further portionof the flu gases issuing from the heater A passes into a heat exchanger 24 whereit serves for heating the fuel delivered by a fan 25 ;wliic'h has toi'be supplied to burners 26, 21,213 of .theconibustion chambers I, 2 and 3 respectively. The remaining flue gases pass into a heat exchanger 29 where they are employed for heating the combustion air required for the burners 26, 2-1, 28 and supplied by a fan 30. The fans 25iand 30 are driven by a motor .3l.

Should the heater for the working medium comprise less or more than 'three heating sur faces connected to oneiano'ther in series in relation'to the direction offfio-w of the flue gasesgthen the fluegases arealso zreturned solely to'the combustion chamber arranged .in 'front of allheating surfaces.

The invention .'is .particularly suited .for application whereLhigh velocities for the combustion gases .;are.adopted;in the heater for the working medium, i. e. when considerable pressure losses occur during the passage of these gases vthrough the heating surfaces. .lnsuch a case it is, on account lot the .power consumption, desirable if the cquantityrof flue gas .which .has :to .be returned to the combustionlcham'berof the heater for'the working .medium can .be kept as small as possible.

What.is-.claimed is:

.1. .In a .high temperature gas-heating ,furnace, the combination of means .forming a plurality of combustion chambersameans forming a plurality of combustion-gas passes, one of the latter leading :from each of said combustion chambers, the combustion-gas pass from each chamber except the ,last .leading to the next combustion chamher .in series; an outlet connection leading from the discharge end of said .last combustion-gas pass; a plurality :ofsurface heatexchange units, each'of said units being mounted within acorrespending combustiongas pass; tubular means connecting said \units ;in:series; means for circulating gas to .be.heated through the .units so connected; i-fuel ihurners .directed into the various combustion chambers; .a branch conduit leading from-said .outletconnection .to the first combustionichamber; :and power driven means for ,propelling gases throughsaid branch conduit toward said chamber, whereby the rheating eifect of each fuel burner upon the exchange unit in the succeedingicombustion-gas passiscontrolledby dilution of its products of combustion with cooler combustion products.

and its tubes extend longitudinally through the corresponding combustion-gas pass.

4. Theicombination defined in claim 1 in which 'eac'hunit of the heat exchanger is multi-tubular .and arranged with its tubes extending 10ngitudinally'through the corresponding combustion-gas pass and the connections are such that th gas to be heated flows through the tubes in counterflow relation to the products of combustion flowingthroug'h said combustion-gas passes.

5. The combination defined in claim 1 in which each innit of the heat exchanger is multi-tubular and arranged with its tubes extending longitudinally through the correspondingcombustion-gas pass and wherein the connections between such heat exchangers are external to the :means enclosing the combustion chambers :and the 011]- bustion-gas passes.

6. The.combinationrdefinedin claiml in which the combustion-gas passes (are substantially vertical zandlarrangediside by-side and (the various combustion chambers other than thefirst are in the form of enlargements interposed in approximately horizontal :connections between the :ends of adjacent combustioneg-as passes.

7. Thetccmbination definediinsclaim 1 in which the combustion-gas :passes are substantially vertical and arranged side bysideand the various combustion chambers other than the first are in the formeof enlargements interposed in approximately horizontal connections between the ends of adjacent combustion-gas passes, the heat exchanger -.units rare multi-tubular and extend each beyond the :ends of the;pass in which :it ismounted, and the connections betweensaid units are external to the means enclosing the combustion chambers'and combustion-igaspasses.

RUDOLF .RUEGG.

REFERENCES CITED 'The following reterencesarebf record in the file of this patent:

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16430.1 Reinhard June .8, 1875 -498;826 :Tilden June 6, 1893 50,300 zcarvalho May 22, 1900 12313.73 J'onsson v iJune 26, 1917 $789,401 Davy -Jan. 20,1931

2,172,910 Keller Sept. E2, 1939 92,174,663 .Keller Oct.23, 1939 2268;074' :Kelle Dec. 30, 1941 1 2,385,177 Wiederkehr. =Sept."18, 1945 2,422,131 .Ruegg .June 10, .1947 

